Abbreviation for precipitation-evaporation quotient.

The temperature at which all three phases of a substance can exist in equilibrium. This temperature occurs at only one pressure. The triple-point of water is 273.16 K and is the basis of the Kelvin scale.

See gain.

The level at which ice crystals and snowflakes melt as they descend through the atmosphere.

A unit of power equal to one joule per second or 10' ergs per second.

Any sudden and heavy rain, almost always of the shower type.

Abbreviation for visual flight rules, but commonly used to refer to the relatively favorable weather and/or flight conditions to which these rules apply.

A thermometer consisting of a clock mechanism the speed of which is a function of temperature.

Same as constant-level balloon.

Same as photometer.

A measure of long-term precipitation effectiveness. The ratio of the normal annual rainfall to the normal annual evaporation.

An instrument for determining the direction of cloud motion. There are two basic designs of nephoscope, the directvision nephoscope and the mirror nephoscope.

An instrument for measuring the extinction coefficient in water.

The inherent imprecision of a given process of measurement, the unpredictable component of repeated independent measurements of the same object under sensibly uniform conditions.

Same as mirror nephoscope.

Any source of radiant energy, especially electromagnetic energy.

A method of streamflow routing which assumes that storage is a linear function of the weighted flow in the reach and is adaptable to a simple mathematical solution.

The effect upon the measurement of rainfall caused by the presence of the rain gauge.

A graphical aid used in fire weather forecasting to calculate the degree of forest-fire danger (or burning index). Commonly in the form of a circular slide rule, the firedanger meter relates numerical indices of (a) the seasonal stage of foliage, (b) the ...

A liquid-in-glass thermometer which uses an organic substance such as alcohol as the thermometer liquid. This type of thermometer has a low freezing point and a high coefficient of expansion. It is less accurate, however, than a mercury thermometer.